Ch. II.] STRATA AT SUCCESSIVE PERIODS. 21 
strata inferior in position to the Subapennines (as e underlies/, 
diagram No. 4). 
No. 4. 
C, Chalk and older formations. 
d, London clay (older tertiary). 
e } Tertiary strata of same age as beds of the Loire. 
f, Crag and Subapennine tertiary deposits. 
This inferior group, e, composed principally of green sand, 
occurs in the hills of Mont Ferrat, and beds of the same age are 
seen in the valley of the Bormida. They also form the hill of 
the Superga, near Turin, where M. Bonelli formed a large col- 
lection of their fossils, and identified them with those discovered 
near Bordeaux and in the basin of the Gironde. 
But we are indebted to M. Deshayes for having proved, by 
a careful comparison of the entire assemblage of shells found in 
the above-mentioned localities, in Touraine, in the south-east 
of France, and in Piedmont, that the whole of these three 
groups possess the same zoological characters, and belong to 
the same epoch, as also do the shells described by M. Constant 
Prevost, as occurring in the basin of Vienna*. 
Now the reader will perceive, by reference to the observa- 
tions above made, and to the accompanying diagrams, that one 
of the formations of this intervening period, e, has been found 
superimposed upon the highest member of the Parisian series, 
d ; while another of the same set has been observed to under- 
lie the Subapennine beds, /. Thus the chronological series, 
d, e, f, is made out, in which the deposits, originally called 
tertiary, those of the Paris and London basins, for example, 
occupy the lowest position, and the beds called • the Crag,' 
and ' the Subapennines,' the highest. 
Tertiary Strata newer than the Subapennine. — The fossil 
Sur la Constitution, &c. du bassin de Vienne, Journ. de Phys., Nov, 1820. 
